Crustal Heat Flow: a guide to measurement and modeling G. R. Beardsmore & J. P. Cull, Cambridge University Press, 2001, ISBN 0-521-79289-4, Hardback, £70, and ISBN 0-521-79703-9, Softback, £24.95

There are not many recent textbooks available devoted to heat transport in the Earth's crust. In particular, since the multi-author Handbook of Terrestrial heat flow Density determination (Haenel 1988) there has been a growing need for an up-to-date monograph which provides an introduction to both data acquisition and interpretation in one coherent text. Thus this new volume is a timely addition to the current literature.

The book is well produced and well printed. As in other Cambridge University Press volumes, a special effort was made to produce all figures in the same style, contributing to the overall uniform and appealing appearance.

The motivation to write this book came to the authors from a discrepancy they perceived in the use and interpretation of geothermal data in the petroleum industry: On the one hand highly sophisticated software for simulating the thermal evolution of sedimentary basins and the maturation of organic material they contain; on the other hand often insufficient appreciation of the underlying physical concepts (and constraints!) and required input data. This defines the particular flavour of the book which puts particular emphasis on the application of geothermal techniques in the hydrocarbon industry. The text contains many question and answers insets which prompt the reader to immediately apply the preceding information. Providing the answers directly following the questions makes self-testing easy for the reader. It would reduce the reader's temptation to read the answer prior to solving the problem, however, if the text of the answers was printed upside down.

Some of the questions may appear rather elementary, when all there is required amounts to plugging numbers into a given equation. On the other hand, this provides the reader with the constant positive feedback of still being with the text. Yet, some of the questions could be more thought-provoking.

The book is organized in three parts: I. The thermal state of the Earth; II. Measurement techniques; III. Modeling Techniques.

Part I has two chapters: Terrestrial Heat and Heat Generation. Chapter One provides a basic introduction to early and later theories on the thermal evolution of the Earth. This is not the most up-to-date part of the book (the most recent reference dates from 1980), and a discussion of more modern literature would have given the book a broader perspective. The discussion of the present thermal state of the Earth is based on the most recent publicly available heat flow data collection, but does not mention Stein's (1995) special discussion of marine heat flow. A particularly helpful table translates the units of the outdated foot-pound-second system, which is still frequently used in the petroleum industry, to the international standard (SI) system of units. Chapter Two introduces the processes of heat generating radioactive decay processes, discusses the concept of crustal ‘heat flow provinces’, and presents methods to calculate the radiogenic heat generation rate from the abundances and densities of uranium, thorium and potassium. Also, methods are discussed to infer the heat generation rate from geophysical borehole logs and from a correlation with sonic velocity. A discussion of other heat generating processes, such as frictional heating along faults and metamorphic reactions concludes this chapter.

Part II has three chapters: Thermal Gradient, Thermal Conductivity and Thermal Maturity. Chapter Three provides a sufficient if not complete outline of direct and indirect temperature measuring techniques, and a detailed discussion of processes affecting the average on-shore and off-shore surface temperature and its variation with geologic time. Unfortunately, the discussion relating to the potential of reconstructing palaeoclimatic variations of the average surface temperature from temperature logs — one of the most productive lines of geothermal research in the past years — is restricted to publications prior to 1997. This excludes many of the newer results and insights published since.

Chapter Four discusses thermal conductivity from theory to measurement techniques (both laboratory and in situ), mixing models for multi-component materials, and derivation of thermal conductivity from a suitable combination of borehole logs. Some of these topics are treated in considerable depth without getting lost in too much detail. In particular I liked the discussion of thermal phonon conduction and its relation to other basic physical properties. At the same time the selection of references is regrettably biased and limited, often omitting more recent sources: a table of thermal conductivity for different lithologies is incomplete without reference to the comprehensive compilations of Cermák & Rybach (1982) and Clauser & Huenges (1995); the dependence of thermal conductivity on temperature is discussed using data from Birch & Clark (1940) without mentioning more recent work of Zoth & Hänel (1988) and Sass (1992); the discussion of heat radiation and the associated concept of a radiative thermal conductivity is based on literature prior to 1969 neglecting more recent papers, e.g. those discussed in the review of Clauser (1988); the discussion of measuring techniques for thermal conductivity unfortunately neglects one of the more recent developments, the non-contact optical scanning method of Popov (1999), which combines high accuracy (comparable to the divided bar method) with a large rate of samples tested; the discussion of in situ methods stops in the early 1970s, again neglecting later work such as Villinger (1985). A more up-to-date treatment would have made this chapter more valuable for readers seeking an introduction. A second edition may provide remedy to these shortcomings. Chapter Five discusses thermal maturity of organic matter. This chapter clearly sets this book apart from preceding heat flow texts as it connects the heat flow and hydrocarbon communities which — for reasons unknown to me — have kept apart from each other to a large extent in spite of a large overlap of interests. A large selection of indirect indicators for maximum palaeotemperature are introduced and discussed in varying detail. A very useful table summarizes the information provided by the different palaeotemperature indicators: the rock types they can be applied to; the equipment required the maturity range they are sensitive to; the palaeotemperature precision; the maximum temperature they yield, as well as their limitations. Again, references offered for in-depth reading often are not the most recent: For instance, no mention is made of the correlation derived between illite crystallinity and maximum temperature by Kosakowski (1999), and the discussion of fission track methods takes no notice of the monograph on this subject by Wagner & Van den haute (1992) which is more recent than much of the literature cited.

Part III has four chapters: Heat Flow, Lithospheric Models, Numerical Modeling, and Unraveling the Thermal History of Sedimantary Basins. Chapter Six discusses how to determine heat flow from temperature and thermal conductivity data by various methods. Much emphasis is put on the discussion of various reasons for a variation of heat flow with depth. These can be brought about by both steady-state and transient effects. In view of the large efforts to extract palaeoclimatic variations of the Earth's surface temperature from suitable non-linear temperature profiles this is a very timely topic. Sources for non-linearity discussed are structural features, such as systematic variations of thermal conductivity, porosity or heat generation rate with depth, and transient effects, such as palaeoclimate, sedimentation, erosion, and heat advection by water flow. With one exception the discussion is on an adequate level, based on standard examples. As before, it does not draw on recent examples and advances in this topic. The exception is the discussion of the effect of groundwater flow. Here the authors argue that vertical fluid flow can be parametrized as an effective increase or decrease in thermal conductivity or in terms of heat sources or sinks. While this is true in terms of heat, it is not in terms of temperature: The corresponding temperature profiles would be quite different in both cases if the mixed conductive and advective heat transport equation was solved. This is an unnecessary source of potential confusion for the non-expert reader and needs to be clarified in a second edition. Heat flow may deviate from the vertical when there are lateral contrasts in thermal properties and the book discusses several structural reasons: basement relief, topography, and salt domes. The chapter concludes with several correlations of heat flow with: heat generation, age, seismic velocity, and electrical conductivity. Chapter Seven discusses the thermal characteristics if different continental and oceanic lithospheric models: stable lithosphere; hot spot; subduction zone; extension zone. Among other topics, this introduces to the marine heat flow versus age and ocean depth versus age relationships, the continental heat flow versus age relationship, and the driving forces for subduction. The discussion of the thermal effect of extension is restricted to the pure shear and simple shear models and does not discuss more advanced concepts and their thermal signatures. Chapter Eight provides a basic introduction to Finite-Difference Modelling of the heat conduction equation. This can serve as a good starter for beginners. However, the authors should have at least mentioned and given reference to two other well accepted numerical methods — Finite Elements and Boundary Elements. The restriction to the heat conduction equation avoids any of the problems associated with numerical solutions of the mixed conductive—advective heat transport equation based on the centred finite difference approximation of the derivative. These problems should at least be mentioned if, for sake of brevity, this topic is not treated individually. The last Chapter Nine applies the content of the preceding chapters to the task of reconstructing the thermal history of sedimentary basins, one of the prime objects of geothermal research in hydrocarbon exploration.

The book offers a large list of references and a useful table of index words. To my impression, the selection of references is a bit biased, and not equally up-to-date across the topics discussed. The book offers a homepage which offers colour versions of the black and white figures in the book, more up-to-date references, and loadable spreadsheets. This is an attractive novel feature which can help to keep a book up to date between editions. It would also enable the authors to provide remedy to some of the shortcomings mentioned above.

This book is a valuable contribution to the geophysical literature. It can serve as a very useful introduction to geothermal research in spite of some minor shortcomings. In its paperback edition it is also certainly a good buy.

References